The principle of blink comparison is well known in the field of astronomy, and optical blink comparators are used to identify anomalous astronomical events. A picture of the sky or portion of the sky at an earlier reference time provides a reference image. Astronomical comparisons are made of the same portions of the sky at a later time for discovering the subsequent occurrence of novae or other celestial events not present in the reference image. According to one prior art method the reference image is placed under one eyepiece of a binocular microscope with the comparison image or data image from a later time under the other microscope eyepiece. The separate patterns before each eye are aligned by stereo vision. The two images superimposed by the eyes of the viewer are alternately illuminated and a variant spot will appear to "blink" and is therefore immediately identifiable. Objects or spots coinciding in both images appear continuously to the viewer.
This stereo comparator requires exact mechanical/optical alignment and is very fatiguing on the eyes of the operator. The operator must also have stereo binocular vision. Such microscope blink comparators therefore are particularly subject to human error. An example of such a microscope optical comparison device is found in U.S. Pat. No. 3,713,720 in which differences between the standard and the object being compared appear as pulsations or flicker in the fused superimposed image. Another example of an optical comparison device is found in U.S. Pat. No. 3,744,917.
The blinking, pulsating or flicker comparison principle has been applied also in projection systems for astronomical application. The projector blink comparator works on the basic "blink" principle, but transparencies are first formed of the reference image and unknown test image or data image for overlapping projection on a screen. The arrays of spots or other elements of the reference transparency and the data transparency are projected alternately onto the screen with careful alignment. The occurrence of unknown or variant spots or elements in one of the respective patterns is identified by the blinking effect in the field of view of the screen. Such a procedure avoids the eye fatigue and strain of the microscope viewer blink comparator but creates difficult optical alignment problems. Furthermore such a projector system is not suitable for other applications in the biomedical field such as protein identification where the spot patterns undergo non-linear distortion during preparation. Thus, the projector blink comparator cannot compensate for varing non-linear distortion across the reference pattern or data pattern causing unintended and undesired differences and variations often encountered in applications in the biomedical field.
One example of a projector blink comparator is available from Ben Mayer, Envel Designs, 1940 Cotner Avenue, Los Angeles, Calif. 90025. Related prior art information may be found in U.S. Pat. No. 4,005,939 and U.S. Pat. No. 3,894,797. A blink comparator designed for astronomers in which the aligned images are presented on a rear projection screen is available from Gaertner Scientific Company, 1201 Wrightwood Avenue, Chicago, Ill. 60614, Model No. M1414.
For applications in the biomedical field such as identifying proteins of an unknown serum, proteins of a known serum and of the unknown serum are each distributed as spots in a separate pattern or array by chromotography and electrophoresis methods such as two dimensional electrophoresis and isoelectric focusing. Such methods introduce non-linear effects and distributions into the pattern or array of proteins which otherwise provide a "fingerprint" pattern of for example as many as five hundred spots used for identifying the unknown serum by characteristic proteins. A disadvantage of the optical and projection type comparators heretofore developed is that because of the non-linearity of the distortions introduced it is not possible to compensate for the distortions over the entire field of view of the optical or projector system for performing the blink comparison.
The complex data handling required for compensation of distortion during comparison has heretofore required complex digital data processing systems such as for example the image data processor described in U.S. Pat. No. 4,254,400; the digital video correlator described in U.S. Pat. No. 4,244,029; and the device for comparing standard and unknown patterns found in the U.S. Pat. No. 4,153,897.
These patents generally describe image or pattern data processors using large computers. For example in U.S. Pat. No. 4,244,029 a reference image and a live image are digitized and the digital signals are compared against each other using digital computer methods. Thus, all three of these references rely on complex computer programs for analysis of data in digital form in order to make the comparison. None of the three references for image processing use the blink comparator principle.